The invention relates to a spring washer for securing screws, nuts or the like, comprising substantially ring-shaped outer and inner washer bodies as well as a transitional region or intermediate section between the inner and outer bodies, the bodies being conical and being open towards the supported side of the washer, and the transitional region having a smaller cross section than the adjoining parts of the inner and the outer washer bodies.
Spring washers serve to counteract loosening of screw joints. Such loosening results from the loss of prestressing forces in the screw joints, and such loss arises as a result of settling and creep in parts being screwed together.
In order to prevent loosening, the spring washers must have a sufficient spring tension across a certain spring deflection which can compensate for loss of the prestressing force, as caused by settling and/or creep, to the extent that is necessary to maintain the clamping force which is required for the operational safety of the screw joint.
For achieving a sufficient spring tension across a certain spring deflection, a great variety of washer constructions have already been suggested. One such construction is disclosed in DE-AS 20 61 297. The transitional region between the washer bodies is formed as a step. In tightening the screw joint, the outer washer body is initially pressed flat against onto the support, on account of which an initial spring tension with a certain spring deflection ensues. With further tightening, the transmission of force results in a very small spring deflection via the relatively stiff step and a relatively high spring tension. On account of the lever action of the step, however, the rim of the outer washer body is lifted off the support in response to further tightening so that the entire load is applied in the vicinity of the step. Accordingly, the region of the support is stressed primarily in this area, which can lead to undesirable damage to the support.
A further spring washer is known from DE-OS 14 00 872. The transitional area between the outer washer body and the inner washer body also consists of a step which substantially leads to the same problems and disadvantages as with the washer according to DE-AS 20 61 297. To prevent loosening of the screw head, this known construction is provided with serrations or corrugations in the region of the inner washer body around the opening for the screw bolt, and the corrugations embed themselves into the material of the screw head to thus produce an additional fastening effect.
In order to avoid damage to the support, it is known to set up an arrangement of a flat, non-resilient washer which lies flat against a support, together with a spring washer which is to be placed above the flat washer. Such an arrangement ensures that the flat washer abuts the support over its entire surface when tightening the screw, while the actual securing effect is achieved by the spring washer. However, the combined height of the washers is considerable and the securing effect is reduced on account of the additional separation line. This known double-washer arrangement also requires a relatively large input of material and leads to assembly problems in arrangements in which a fastening screw is to be mounted jointly with the double-washer arrangement.